1. Field of the Invention
The present invention relates to a polishing pad conditioning apparatus in a chemical mechanical polishing (CMP) apparatus. More particularly, the present invention relates to a polishing pad conditioning apparatus in a CMP apparatus configured to reduce abnormal wear (abrasion) of the polishing pad.
2. Description of the Related Art
A highly integrated semiconductor device has a multi-layered stack structure. Accordingly, it is necessary to perform a polishing process for planarization of each layer formed on a semiconductor wafer in the manufacture of a semiconductor device. A chemical mechanical polishing (CMP) process is a generally accepted polishing technique. The CMP process provides excellent planarity in planarization of both narrow and wide areas, and is advantageously applied to larger wafers.
In the CMP process, the wafer surface, coated with tungsten or oxide, is polished by both mechanical friction and a chemical slurry, thereby achieving a high degree of polishing. Mechanical polishing is used to polish the wafer surface by abrasion between the polishing pad and abrasive particles in the slurry and the wafer surface. The mechanical polishing is further accomplished by rotating the polishing pad in a state in which a wafer fixed to a polishing head is pressed against the surface of the rotating polishing pad with the abrasive particles interposed therebetween. Chemical polishing is used to polish the wafer surface using a slurry as a chemical slurry supplied between the polishing pad and the wafer.
In the planarization technique using the CMP apparatus, the surface state of the polishing pad of the CMP apparatus is an important factor in determining the characteristics of the wafer surface, such as uniformity, planarity or roughness. In the continuous polishing process, the abrasive or other kinds of foreign matter accumulate on the polishing pad, and the polishing pad may become damaged due to these materials. Consequently, the surface of the polishing pad experiences a change in its surface state, causing deterioration to the planarization stability.
Thus, in order to maintain a stable surface state of a polishing pad in performing a continuous planarization process on a wafer using a CMP apparatus, various kinds of polishing pad conditioners and conditioning methods using the conditioners have been proposed.
A generally known conditioning method of a polishing pad includes abrading the surface of the polishing pad with a conditioner formed by embedding diamond particles in a circular plate made of a nickel and iron alloy and evenly conditioning the entire surface of the polishing pad.
FIG. 1 illustrates a schematic plan view of a conventional CMP apparatus that is most typically used.
Referring to FIG. 1, a disc-shaped polishing pad 1 is mounted on a rotation plate (not shown) and rotates in one direction, and a conditioner 2 is positioned thereon. The conditioner 2 rotates in the same direction as the polishing pad 1 by means of a separate rotation device and is moved across the polishing pad 1 from a portion near its center region to its peripheral region, by means of a rotary arm 3.
The conditioner 2, as shown in FIG. 3, has polishing particles 2b, such as diamond particles, embedded into the bottom surface of a metal base 2a. The conditioner 2, as shown in FIG. 2, is fixed to the bottom surface of a conditioner head 4. The conditioner head 4 is fixed to the bottom surface of the leading end of the rotary arm 3 and is rotated by a motor 5 mounted thereon.
Since the conventional CMP apparatus is configured to polish the polishing pad 1 by means of the rotating conditioner 2 which moves across the surface of the polishing pad 1 by the rotary arm 3, a nonuniform surface may result from a difference in the amount of material polished (also termed wear amount or removal rate) according to position, as illustrated in FIG. 4. That is to say, since the innermost and outermost parts of the polishing pad 1 are not ranged over by the conditioner 2, conditioning is insufficiently performed at those parts. On the other hand, the center region of the polishing pad 1 is fully ranged over by the conditioner 2, thereby producing sloping portions. As a result, the conditioned area of the pad is reduced across the whole polishing pad 1, which can be explained by the following empirical relationship known as Preston""s equation:
Removal ratexe2x88x9dLinear velocityxc3x97Pressurexe2x80x83xe2x80x83(1) 
Equation (1) indicates that the wear amount is proportional to the product of the pressure and the relative linear velocity between wafer and pad, at a given position on the pad, for constant operation time.
According to equation (1), as shown in FIG. 5, a difference in the amount of polished pad material is exhibited between the center region and peripheral region of the polishing pad, which is because the linear velocity decreases toward rotation center region of the polishing pad and increases toward the peripheral region thereof.
Korean Patent Application 96-59185 discloses a technique in which a conditioner for polishing a polishing pad is configured to have polishing particles distributed at different densities with respect to position on the polishing pad. This technique is intended to decrease the wear rate at the center of the range covered by conditioner to thus eliminate the sloping portions due to incomplete polishing at the center and peripheral regions of the polishing pad, as shown in FIG. 4. However, while conditioning according to this technique partially solves the problem of incomplete polishing, it cannot solve the problem of nonuniform polishing due to a difference in the relative linear velocity.
To solve the above problems, it is a feature of an embodiment of the present invention to provide a polishing pad conditioning apparatus in a chemical mechanical polishing apparatus, by which uniform conditioning can be achieved across the polishing pad by reducing a local difference in the amount of polishing pad material removed during conditioning depending on a difference in the linear velocity of the polishing pad.
It is a second feature of an embodiment of the present invention to provide a polishing pad conditioning apparatus in a chemical mechanical polishing apparatus, by which the effective conditioned area on the polishing pad is extended.
It is a third feature of an embodiment of the present invention to provide a polishing pad conditioning apparatus in a chemical mechanical polishing apparatus configured to simultaneously perform a CMP process for a wafer and a conditioning process for the polishing pad.
Accordingly, to provide for the first feature, there is provided a polishing pad conditioning apparatus including a conditioning plate which maintains a predetermined relative velocity with respect to the polishing pad, extends from a center region near a rotation center of the polishing pad to a peripheral region near an edge of the polishing pad, and has a polishing portion with polishing particles embedded into its bottom surface, a force generating portion for applying a force to the conditioning plate so that the conditioning plate presses against the polishing pad with pressure that varies according to position on the polishing pad, and conditions the polishing pad by relative linear velocity and pressure with respect to the polishing pad, and a supporting portion for supporting the force generating portion.
Preferably, the force generating portion is configured to apply a force to the conditioning plate so that the conditioning plate presses against the polishing pad with a pressure decreasing linearly or non-linearly across the polishing pad from its center region to its peripheral region.
The polishing portion is preferably semicircular-cylindrically shaped.
The force generating portion may include a housing enclosing a compressed air chamber and having a compressed air injecting portion at its one side, and an expanding portion provided in the lower opening portion of the housing, and having a membrane deformed by the pressure inside the housing to press the conditioning plate and a frame for supporting the membrane. A slot, which permits deformation of the membrane, is preferably provided in the frame of the expanding portion. In particular, the width of the slot formed in the frame of the expanding portion preferably decreases, linearly or non-linearly, from the center region to the peripheral region of the polishing pad
In the chemical mechanical polishing apparatus according to an embodiment of the present invention, the supporting portion preferably supports the force generating portion at its one end, and its opposite end is preferably a load portion rotatably fixed to the platform positioned at one side of the rotation plate.